The effect of increased concentrations of calcium (Ca) (3-24 mM) and boron (B) (100-800 PM) in the medium was studied on the occurrence of shoot tip necrosis (SIN) in cultures of Pistacia Vera L. STN was significantly reduced by application of Ca or B, however media with more than 200 PM boron had reduced shoot multiplication. Ca (12-24 mM) supplied as calcium chloride reduced STN without any adverse effect on shoot multiplication or elongation, whereas calcium acetate reduced elongation. It is concluded that STN is a physiological mineral disorder associated with Ca and/or B deficiency in the meristematic regions of actively growing shoots. Application of Ca (up to 24 mM) as calcium chloride to the medium was the best treatment for the control of STN. Reduction of humidity or increased aeration in the culture jars did not have any significant effect on the occurrence of STN.Abbreviations: MS = Murashige and Skoog medium; STN = Shoot tip necrosis

A rapid and simple method for adventitious shoot regeneration and somatic embryogenesis from immature cotyledon explants of pea (Pisum sativum L.) is described. Cotyledon size and the explant orientation to the medium surface were shown to have a clear effect on shoot regeneration. The highest frequency of shoot regeneration was achieved when the distal end of the greenest cotyledons (7-8 mm in size) were placed in contact with the agar surface. Shoots rooted at a frequency of 80-90% and grew into normal fertile plants. Somatic embryos were induced in cultures of immature cotyledons on modified MS medium containing high levels of a-naphthaleneacetic acid (27-215 I~M) and 2,4-dichlorophenoxyacetic acid (23-181 p~M). A higher frequency of somatic embryos with a normal morphology were induced using a-naphthaleneacetic acid.

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